This invention relates to the field of elution. More specifically it relates to a method and system for producing an eluent having a known concentration of different liquids. More specifically still, it relates to a method and system for producing an eluent having a time varying concentration of different liquids.
The simplest elution system, used for example in a chromatographic column, supplies an eluent comprising a single liquid to the column. In many instances, however, this single liquid is not effective in removing all of the desired material from the column, and a second liquid must subsequently be supplied. Alternately, an eluent having a set concentration of the two liquids is used. More than two liquids can and have been used, but for convenience in describing the prior art and our invention, we will limit the discussion that follows to a system using two liquids which we will label liquid A and liquid B. Switching liquids in mid-operation and the use of a mixture of liquids have not been favored procedurally, and there has been a recent tendency to gradient elution systems. In gradient elution, the initial eluent contains a set concentration of the liquids (usually 100 percent A and none of B), and this concentration is slowly altered, through intermediate concentrations, to a second set concentration of the liquids (usually none of A and 100 percent of B). The conventional way of doing this is to use two constant flow pumps. One of these pumps pumps liquid from a pot containing liquid having the initial concentration of the two liquids (usually 100 percent of A and none of B) to the column. The second pump pumps liquid having the desired final concentration of the two liquids (usually none of A and 100 percent of B) into the pot provided for the first pump so that the concentration of liquid in the pot which is being pumped to the column, gradually changed to the final concentration. This procedure has several disadvantages. Two pumps are necessary, and although the change in concentration can be fairly precisely controlled, the system is not versatile in terms of the ability to tailor changes in concentration, to meet the needs of individual tests. In some instances, instead of using the two stage system described above, two proportional flow valves are used in combination with the two pumps, and the flow of liquid through the valves is varied to achieve the desired concentration. This system suffers from the fact that the flow through proportional valves is difficult if not impossible to control with any precision, especially at low flow, so that the concentration cannot be controlled precisely.
It is an object of the present invention to provide a method and system for providing an eluent in which the concentrations of the liquid parts is precisely known. It is a further object of the present invention to provide an eluent having precisely controlled time varying concentrations of the liquid parts. It is a still further object of the present invention to provide a system for producing an eluent having time varying concentrations of liquid parts in which the means for controlling the concentration of liquids provides for flexible control over the concentrations of the liquids in the eluent and over the rate of change of those concentrations. It is another object of the present invention to provide a method and system for producing an eluent having a time varying concentration of liquids, in which a single pump is used.